Seasonal shifts in the vertical distribution of fish in a shallow coastal area

Depth structures aquatic habitats, creating substantial differences in the species composition of underwater communities even at small intervals. Those communities also undergo considerable cyclic variation annually. In this study, we surveyed variation in the vertical distribution of fish in a shallow (20 m) coastal basin in the northern Baltic Sea during the ice-free period from May to October. The waters were strongly mixed throughout the season and only transient signs of stratification were observed. As production shifted towards higher trophic levels over summer, with sequential biomass peaks in zooplankton and juvenile fish, the vertical distribution of the entire fish assemblage became increasingly even. The results suggest that spatial resource partitioning can be strongly correlated with seasonal productivity cycles even in physically uniform environments with high connectivity. Further, the results stress the importance of sampling design (seasonal and vertical coverage) of fish studies in shallow coastal areas.

Spatial resource partitioning by sympatric grey fox (Dusicyon griseus) and culpeo fox (Dusicyon culpaeus) in southern Chile

The activity patterns, home-range use, and habitat utilization of sympatric South American grey fox (Dusicyon griseus) and culpeo fox (Dusicyon culpaeus) in eastern Torres del Paine National Park, Chile, were studied to determine how the two species were distributed. Both species were primarily nocturnal. Mean percent daily activity did not differ between species or among seasons, but the grey fox had a greater daily activity rate in summer and fall and the culpeo fox in winter and spring. Seasonal and annual home ranges of culpeo foxes were larger than those of grey foxes, but did not differ between sexes or among seasons. Home ranges of grey and culpeo foxes were interspersed in a mosaic-like arrangement and did not overlap. Grey foxes were located more often in upland shrub transition habitat and in areas of medium cover density. Culpeo foxes were found more often in thickets of trees and in areas of high cover density. Within their home range, matorral shrubland or Nothofagus thicket habitat was selected by all culpeo foxes and by 60% of grey foxes monitored. Interference competition by the culpeo fox may have been important in determining fox distribution.